My gods, Wrath of Ashardalon is fun. It’s hard, but it’s accessible, varied, quickly set up, and just the right amount of fast. There’s none of the set-up fiddliness of the “wide open” adventure games (like Runebound and Return of the Heroes, where you carefully place chits or tokens across a board), and solo play does not need a timer to be press you to engage early and often, since monsters engage with you all by themselves.
And now, gallery!
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Spontaneous ∂erivation 
I dearly love Wrath of Ashardalon. It’s actually not quite as hard as Castle Ravenloft, which tends towards fewer treasures and more vicious random events, but that seems to be a pretty deliberate atmospheric choice: sword & sorcery fantasy vs. horror fantasy. (You can, in theory, combine bits, but given the way the adventures are set up, I generally don’t bother, except for the PC options.)